At the Dawn of Continents: Archean Tonalite-Trondhjemite- Granodiorite Suites

Archean rocks of the tonalite-trondhjemite-granodiorite (TTG) suite are dominant constituents of Earth’s earliest preserved silicic crust, while conversely rare in Phanerozoic continental crust. Their formation represents the first critical step towards the construction and preservation of continents. Formation of most TTG magmas involved partial melting of hydrous, probably silicified, mafic rocks at various depths (20–50 km, possibly up to 100 km). Many possible tectonic scenarios fit the petrological and geochemical constraints on TTG formation, whether compatible with a global plate tectonic- like regime or not. Refining such scenarios is a major challenge that requires systematically integrating the constraints on TTG formation—relying especially on accessory minerals as key petrogenetic tools—with the geological context on a regional scale.